Microemulsions of high molecular weight, quaternized Mannich polyacrylamides are well known as taught in U.S. Pat. Nos. 4,956,399; 5,037,881 and 5,132,023 as well as methods for their production and use to dewater dispersions of suspended solids.
These microemulsions have proven to be very commercially successful, particularly in the dewatering of municipal and industrial sludges such as sewage sludge. The high molecular weight of the quaternized Mannich polymers and the capability of controlling the concentration of the quaternized aminomethyl groups of the polymers have contributed to the products' success.
One of the problems experienced by these microemulsions, however, is their relative inability to dewater suspended solids dispersions which are of low solids content. Dispersions of suspended solids of lower solids content require dewatering additives which possess a higher Standard Viscosity than those commonly employed in some dewatering applications. That is to say, most high molecular weight, quaternized Mannich polymer microemulsions commercially sold possess a Standard Viscosity of about 3.0 cps. and below and, as such, are not as effective for dewatering low solids dispersions as would be desired.
High molecular weight, quaternized Mannich polymer microemulsions are prepared by reacting an (alk)acrylamide polymer backbone, in microemulsion form, with formaldehyde and a secondary amine, usually in the form of a complex, e.g. N,N-dimethylaminomethanol, and then quaternizing the resulting Mannich polymer base. During the reaction of the backbone with the formaldehyde/secondary amine to form the Mannich, the Standard Viscosity of the resultant Mannich polymer microemulsion is normally equal to or slightly greater than that of the starting (alk)acrylamide polymer backbone microemulsion. However, further reaction of the Mannich polymer base with the quaternizing agent reduces the Standard Viscosity of the microemulsion of the quaternized Mannich polymer to a value below that of the original backbone polymer microemulsion.
Because of the loss of the Standard Viscosity (S.V.) during the quaternization of the Mannich polymer, it has usually been the case to attempt to make the Standard Viscosity of the backbone polymer as high as possible. This has usually been accomplished by employing the amount of chain-transfer agent which enables the production of the optimum Standard Viscosity of the backbone polymer which is not subject to drastic reduction during the quaternization procedure. It has been found that the S.V. of the quaternized polymer microemulsion falls off on both sides of this optimum concentration of chain-transfer agent i.e. a plot of the S.V. and chain-transfer agent concentration is parabolic-like in shape. Thus, there is a limit as to the highest S.V. which can be attained for each and every polymer backbone using this production procedure.
Because the quaternized, Mannich polymer microemulsion is comprised of much more than the polymer per se i.e. emulsifier, water, oil, etc., the tendency has also been to produce the quaternized, Mannich polymer microemulsion at as high a polymer solids content as possible so as to save on costs of shipment. Thus, the polymer solids content is normally over 42% by weight, of the aqueous phase of the microemulsion. At such high polymer solids content, the Standard Viscosity of the resultant microemulsion attainable is restricted.
Since the Standard Viscosity of the microemulsion of the quaternized, high molecular weight polymer should be as high as possible for many applications, and since it is very difficult to prepare (alk)acrylamide polymer backbone microemulsions at higher Standard Viscosities, the need exists for polymers of high molecular weight, quaternized Mannich polymer microemulsions having standard Viscosities which enable them to effectively dewater low solids containing dispersions, i.e. those having Standard Viscosities above about 3.3 cps.
The ability to supply high Standard Viscosity, quaternized, Mannich polymer microemulsions which effectively dewater low solids-containing dispersions would provide a benefit to industry which would receive favorable recognition and acceptance.